This invention relates to float actuated liquid level indicators, and more particularly to such indicators employing a string of many Hall-effect switches actuated by a floating permanent magnet.
It is well known to indicate liquid level by a floating permanent magnet actuating one or more of a plurality of Hall-effect switches disposed in a vertical array. U.S. Pat. No. 5,565,687 issued Oct. 15, 1996 to Berrill reviews the prior art. He discloses a linear series of Hall-effect switches disposed in a plurality of linear vertical arrays in discrete probes which are butted end to end. In each array a resistance chain is linked at intervals to the switches. Movement of the floating magnet adjacent the array thereby gives a progressively changing voltage on an output line from the resistance chain. When the magnet moves from one array to the succeeding array, after generating a maximum signal , that signal is maintained by a latch. A cumulative signal from the series of latches can then be generated. The arrays are powered separately in parallel so that the length can be extended as desired by additional arrays. The object is to reduce error due to noise over useful signal as the number of switches is increased to increase resolution and/or the length of the device. For liquid level indicators encircled by a floating magnet a practical problem with increasing resolution for a fixed length of indicator is the actual physical dimensions of the switches. If the minor dimension of the switch is, for example, 5 mm, then at most only 100 switches may be disposed in a vertical array for a tank with a 50 cm depth. This limits resolution to 1% of the volume. It would be useful to be able to obtain finer resolution with vertical arrays of switches. As the actual cost of these switches is steadily diminishing, the use of increasing numbers of switches would be a viable alternative if there were a way of overcoming the problem of geometry.
It is accordingly an object of the invention to provide a liquid level indicator that employs a floating magnet actuating a vertical array of Hall-effect switches in which the number of switches in that array can be greater than that dictated by the vertical dimension of the switch. This is achieved in the instant invention by positioning each switch beside its preceding and succeeding switches and spaced apart vertically therefrom by less than the vertical dimension. The switch array is then wrapped around into a closed cylinder or similar configuration to form a stair step or helical array of the switches. The floating magnet is arranged to provide equal magnetic effect on all of the switches as it rises and falls. This may be achieved by an encircling annular magnet, for example, or by a magnet floating within the cylinder. Various means are provided to reduce the effect of signal noise.
These and other objects, features, and advantages of the invention will become more apparent when the detailed description is studied in conjunction with the drawings in which like elements are designated by like reference characters in the various drawing figures.